Those skilled in the art will appreciate that a variety of exhaust manifolds, catalysts and mufflers have been used in automotive vehicles. Although designers have attempted to combine a catalyst with an exhaust manifold, as shown in U.S. Pat. No. 3,937,015 (Akado et al.), and other cited references, such designs are generally not compact and therefore lacking in usefulness under the hoods of modern automotive vehicles in which space is at a premium. A system according to the present invention provides superior processing of exhaust gases due to the turbulent flow through the substrate, as well as exhaust noise attenuation capability. The present system provides improved gas treatment because the design provides greater catalytic surface area and the gases are carefully guided through the catalytic element such that the flow of exhaust gases passes evenly through the substrate, providing superior treatment results.